The present invention relates to a variable mask device for an illuminator or the like, and more particularly to a variable mask device wherein a luminous area provided by the illuminator or the like can be definitely outlined or focussed in an optical manner in conformity with an area to be illuminated, as projection frame lines in a slide projector or the like. Said definitely outlined luminous area can be varied both in size and shape, for example, into a square, rhombic, trapezoidal or circular shape, for effective spot illumination within an ordinary room, for example, an exhibition hall or the like.
Variable mask devices of this general type are well known from, for example, utility model publication 48-37507 by the applicant, wherein the variable mask device comprises a pair of support frames each having a central opening defining the projection window interposed between the source lamp and the projector lens of the illuminator and secured at four corners, integrally to the body of the illuminator so that four mask plates may be slidably inserted between said pair of support frames from four sides thereof substantially toward the center of said projection window and may be rotated to obtain a luminous area of desired size and shape.
However, with such a prior art device, it is difficult to focus the outline of the luminous area defined by the mask plates over the total area to be illuminated when a framed picture hung on the wall, for example, is illuminated obliquely from above. To overcome such a problem, it has already been well known to provide two sets of mask plates a predetermined distance, spaced apart from each other along the projection axis. Although the problems have been improved to some degree, it still remains impossible to focus, for example, a projected image of a slide or the like, inserted into the projection window, over the total area to be illuminated.
Accordingly, an object of the present invention is to provide a variable mask device for an illuminator or the like, by which the light image can be focussed over the total area to be illuminated, even when said area to be illuminated is inclined with respect to the projection axis.
Another object of the present invention is to provide a variable mask device permitting an outline of the luminous area formed by the variable mask plates to be freely rotated around the projection axis, thereby overcoming the drawback of the prior art devices that it is restricted and difficult to rotate and slide the four variable mask plates and thereby to rotate said outline around the projection axis.
Still another object of the present invention is to provide a variable mask device for an illuminator or the like which is adapted to simultaneously achieve the above defined objects.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.